The research proposed is an analysis of the types of intercellular communication used by the nervous system in the control of behavior. One preparation used is the marine mollusc, Aplysia. Chronic recordings will be made in intact animals to study the link between neural plasticity and long-term changes in behavior. A second project will involve an examination of the neural circuitry underlying reproductive behavior of Aplysia. The third project is a study of neuroendocrine function in Aplysia, using the bag cells as a model system for investigation of the electrical activity in acute and chronic preparations and of the chemistry of the bag cell hormone. Synaptic transmitters will be measured either in single cells or following release by a new technique described in the fourth project. The uptake of transmitter by glia after release from neurons and trophic effects of glia on vascular tissue will be examined in project five. The release of transmitter by pharmacologic agents is the subject of the sixth project. The neural control of swimming behavior of elasmobranchs and of the electric discharges of a fish electric organ will be examined in project seven. The regulation of the circulation by the nervous system is the theme of the eighth project. Finally, the last project is concerned with the functional meaning of a previously ignored group of unmyelinated fibers in ventral roots. The program of research utilizes an interdisciplinary and comparative approach to the solution of problems and takes advantage where appropriate of certain marine forms to serve as model systems. The unifying theme among the projects is cell to cell communication including but not limited to neuronal circuitry.